The present invention relates to a method for stuffing a monolith with a mounting mat into a housing, wherein the monolith is wrapped with the mounting mat.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Catalytic converters and diesel particulate filters typically include a housing in which a catalytic converter or diesel particulate filter is arranged as a monolith. The monolith is usually composed of a filter body, for example made of a ceramic substrate. A mounting mat is placed around the monolith. The mounting mat has a function comparable to a spring. The mounting mat is used to keep the monolith stationary in the housing at different temperatures and under different load conditions. When the mounting mat is a swelling mat, the mounting mat does not swell at cold temperatures. The mounting mat must nevertheless securely hold the monolith. At warm temperatures, the mounting mat usually swells due to the heat more than the housing expands, without causing the forces which act on the monolith to damage the monolith. In addition, the monolith, the mounting mat and the housing must have all the tolerances with respect to size, circumference and/or thickness. The housing diameter is defined within the context of tolerance deviations, as is the diameter of the monolith. Only the mounting mat is able to compensate deviations within the tolerance limits due to its spring effect, but only up to a certain degree. If the mounting mat is compressed too much, meaning overpressed, it is permanently damaged. Ideally, the mounting mat would be compressed only up to its optimum spring action, so as to apply just enough force to hold the monolith in the housing. However, the mounting mat is frequently subjected to substantially higher pressures during stuffing. If lower compression forces could here be applied, the quality and durability of the catalytic converter would be increased, and costs could potentially be reduced by using a thinner mounting mat. Another problem associated with stuffing into a prefabricated housing is that even housings with circular cross-sections do not have a perfect circular cross-section, with deviations from the ideal cross section present within the tolerance variations. The problem is exacerbated when the prefabricated housing has a non-circular cross-section. When the housing and the monolith wrapped in the mounting mat are positioned relative to each other for stuffing, rotation of the housing and/or monolith relative to each other cannot be excluded. Even a slight rotation of 1° to 2° can cause the mounting mat to contact the housing wall at a point of the cross section and thus be sheared during stuffing. Overpressing or shearing of the mounting mat must hence be prevented when the monolith wrapped in the mounting mat is stuffed into the housing, because the lifetime of the catalytic converter and diesel particulate filter would otherwise be reduced. On the other hand, the housing must not be so large that the monolith has play.
It would therefore be desirable and advantageous obviate prior art shortcomings and to provide an improved method for stuffing a monolith wrapped in mounting mat into a predetermined housing a stuffing funnel with the smallest possible error and with the least damage to the catalytic converter or diesel particulate filter.